1. Field of the Invention
The present invention relates to a pulp-like composite material and a process for production thereof. More particularly, the present invention relates to a pulp-like composite material excellent in heat resistance, electrical insulation, dimensional stability and mechanical properties, as well as to a process for production thereof.
2. Prior Art
Of pulp-like materials, wood pulp is best known. Wood pulp is widely used as various paper products and also is used in a large amount as electrical insulating papers, etc.
Wood pulp, however, not only possess big drawbacks of high hygroscopicity, low heat resistance, poor dielectric property, etc. but also are unable to satisfy the requirements (e.g. heat resistance, electrical insulation, dielectric property) for smaller-sized and lighter weight electric apparatuses and appliances, i.e. electric motor, generator, transformer, etc. of smaller size and lighter weight.
Meanwhile, asbestos is used in many applications such as friction material (which is used in, for example, the brake lining, clutch facing, etc. of automobile), high-temperature gasket, packing, filtering material, building material and the like. Asbestos has problems of future unavailability due to exhaustion of asbestos resource as natural mineral and adverse effect on health due to dust generation. Hence, various attempts have been made in order to develop a substitute material for asbestos. That is, in the field of, for example, a friction material, an attempt is under way to use, as a substitute component for asbestos, a fibrous material other than asbestos, such as glass fiber, steel fiber, rock wool, carbon fiber, aramid fiber or the like.
However, the above substitute fibers for asbestos, having no pulp-like structure as possessed by asbestos, have problems in miscibility with other friction material components, productivity, etc. in production of friction material; further, the friction materials using the above substitute fibers for asbestos are insufficient in friction properties, mechanical strengths, etc.
It was also attempted to produce a pulp-like material by mixing an above-mentioned substitute fiber for asbestos, with an inorganic substance powder using a rubber or a thermoplastic resin; however, the resulting pulp-like material has a low heat resistance of 200.degree. C. or below and is insufficient. To improve the heat resistance, an aromatic polyamide was used as the resin; the resulting pulp-like composite material, however, was inferior in compatibility with other materials, adhesion, etc.